Conventional fluid flow detecting devices are intrusive or non-intrusive. Intrusive devices are positioned within the pipe through which the fluid flows. For example, a turbine may be positioned within the pipe which turns in the presence of fluid flow to generate an output signal. Such intrusive detection devices include moving parts which disturb the flow and typically are expensive. Accordingly, it is an object of the invention to provide an economical flow detection apparatus which does not require moving parts.
The conventional non-intrusive fluid flow detection device measures the doppler shift of a sonar signal. Typically a transmitter is positioned on one side of a pipe while a receiver is positioned on the opposite side. When fluid flows within the pipe, the moving medium alters the frequency of the transmitted signal doppler shifting the sonar signal's frequency. Such doppler shift measuring devices are complex and expensive. Accordingly, it is an object of the invention to provide a simple inexpensive fluid flow detection apparatus.
According to the present invention acoustic principles are used to distinguish sounds generated by the flow of fluid through a select pipe from other pipes. Fluid flow is detected by two sound transducers with the transducers being positioned relative to the select pipe such that the sounds generated from the select pipe are in a known phased relationship. For example, by spacing the transducers at one half wavelength, the signals detected corresponding to the flow through the select pipe are in phase. Sounds from fluid flow in other pipes, remote fluid sounds, will travel through the pipe reaching one transducer first, then the other one half wavelength later. As a result the remote sounds are 180 degrees out of phase. Other sounds having frequencies other than the known frequency of the fluid flow are filtered out. In addition, the background noise is monitored to distinguish inadvertent background noise.